×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Decoupling fundamental frequencies of PCB and chassis using Steinberg Octave Rule

Decoupling fundamental frequencies of PCB and chassis using Steinberg Octave Rule

Decoupling fundamental frequencies of PCB and chassis using Steinberg Octave Rule

(OP)
Hi guys,

Just a question regarding PCB and PCB enclosure/chassis design. Steinberg states that the fundamental frequency of the PCB and chassis be decoupled by an octave or greater but mentions noting of PCB/Chassis relative orientation or mass participation.

For example: If I mount a PCB parallel to a simply supported beam. I am comparing the Mode 1 for each, which, due to their shape and support is in Z direction for both (BTW using same coordinate system for both).

Lets say that I don't achieve decoupling, Mode 1 for beam is 600 Hz and Mode 1 for PCB is 600 Hz both modes in Z -direction.

If I now change design and have the PCB mounted perpendicular to the beam. Its critical axis is now in X-axis and at 90 degrees to the beam. Mode 1 for PCB is still 600 Hz but in X-direction and Mode 2 for PCB is in Z-direction and is 1200 Hz.

Question is: is PCB and chassis coupled because Mode 1 for PCB = Mode 1 for beam or is it decoupled because Mode 1 for beam is 600 Hz in Z-direction and the corresponding Mode (Mode 2 in Z direction) of PCB is 1200 Hz?

Thanks in advance,

Mark

RE: Decoupling fundamental frequencies of PCB and chassis using Steinberg Octave Rule

You may get some reduction in response but you'll still have a strong 600 Hz resonance. Mode shapes don't understand our puny 3 axis coordinates, they are really energy flows, and have no trouble going round corners.

A factor of 2 on frequency separation is rather an excellent criterion, half that is good enough (a highly damped system may have enough bandwidth for 50% separation to be insufficient, but highly damped systems aren't the problem).

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Decoupling fundamental frequencies of PCB and chassis using Steinberg Octave Rule

(OP)
Thanks Greg,

I thought this much since the orthogonality of the respective modes is never mentioned!

Do you know of a source for proof of this? Book, publication or something else I can reference?

Kind regards,

Mark

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources